For many years, liquids have been stored in cylindrical tanks having roofs buoyantly supported by the liquid. One problem which exists in many such storage tanks is to provide a sliding seal between the roof and tank walls so as to prevent escape of vapors from the tank. The problem becomes particularly acute when the liquid stored in the tank is petroleum or is one of a variety of petrochemicals.
Many arrangements have been suggested to provide a seal between the floating roof and the walls of the tank. These arrangements normally take the form of an elongated, hollow, inflatable tube disposed along the edge of the floating roof. The seal is formed by pressurizing the tube to cause it to fill in the space between the roof and walls of the tank. One problem arises from this seal when sufficient pressure is supplied to the tube to cause it to accommodate variations in wall shape, e.g. "ovaled tanks". This high pressure results in excessive friction between the tube and the normal tank walls thereby affecting the buoyancy of the roof. Another problem is caused by punctures occurring in the tubes. These punctures occur because of the direct contact between the tubes and the wall; such as, from sharp edges existing in the wall and from wear developing as the roof moves relative to the wall.
Accordingly, it is the primary object of this invention to provide a seal for a floating roof tank that will accommodate considerable variation in tank configuration without resulting in excessive friction.
Another object of the invention is to provide a seal for a floating roof tank which compensates for seal wear without a change in the fluid pressure.
Another object is to provide an inflated tube type seal which is not susceptible to damage or puncturing by sharp edges or the like on the tank wall.
In accordance with the invention, apparatus is provided for a seal in a floating roof tank. The seal uses at least one expandable tube having an extended lip with sufficient length and thickness to provide a resilient reaction when deflected in a direction toward the expanded tube. At least one clamp is attached to the roof and partially encloses the tube for restricting movement of the expanded tube away from the wall. A sufficient fluid pressure is supplied in each tube to expand the tube and cause the lip to deflect when contacting the wall in a generally spiralling direction around the tube which prevents substantial vapor losses from any liquid stored within the tank.